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View the documentIn brief

African tree's seeds could replace expensive chemical water purifiers

Crushed seeds from an indigenous African tree could replace high-priced, imported chemicals as a water-purifier, according to a team of British researchers, who have launched an experiment in Malawi to prove their point.

The idea originally came from Sudan, where families use Moringa tree seeds to clear spring water in large earthenware jars. Now, after six years of interdisciplinary research on the properties of the seeds of the Moringa oleifera and Moringa stenopetala species, researchers from Leicester University have set up a unit at Thyolo in southern Malawi to treat 48 cubic metres of water a day. The program is being carried out in collaboration with local authorities, supported by the British Overseas Development Administration (ODA).

"The crushed Moringa seeds can clear very turbid water", John Sutherland of the university's Department of Environmental Technology said. "Indeed, the crushed seeds coagulate particles suspended in water as well as certain types of (bacteriophagic) virus. The combination forms agglomerates, which then fall to the bottom where they can be collected".

But Sutherland said further disinfection still is needed before the water is fit for human consumption. Although the seeds can effectively eliminate a significant percentage of indigenous bacteria by coagulation and flocculation, the treated water should be further disinfected by slow filtration or chlorination at the treatment site, or boiling in the household.

Both M. oleifera and M. stenopetala are widespread in semi-arid subtropical countries, and their seeds are harmless to humans. In Malawi, the pods, flowers and leaves of the tree, known locally as the Chamwamba, are the basic ingredients of the traditional local dish Ndiwo.

Moringa seeds have both economical and ecological advantages over chemicals. Malawi not only could save US$460 million a year if it no longer needed to import alum (aluminum sulphate) to purify its water but might also be able to start cash-crop production of the seeds to stimulate the local economy. Planting the trees would help stabilize soil and contribute to the fight against deforestation.

Highly drought-resistant

The Moringa tree is highly resistant to drought and needs little care. It is fast-growing, produces its first seeds at 18 months and lives for an average 50 years. Each tree can produce approximately 10 000 seeds a year, and one hectare of Moringas spaced two metres apart would provide enough seeds to clarify 250 cubic metres of water every day of the year.

Working first on artificially polluted water in the laboratory and then on small volumes of water taken from three rivers in Malawi, the British research team estimated the quantity of seeds needed depending on the turbidity of the water and the volume to be treated. They found that 100 milligrams of crushed seed can clear one litre of very turbid water.

The small experimental unit built in Thyolo will be the first attempt in Malawi to treat water with Moringa on an industrial scale. The method is simple and involves traditional operations. The seeds, obtained from a trial plantation of 4 500 trees, will be dried in the sun, crushed and sieved. The water, diverted from the Thyolo River, will be treated continuously in a rudimentary facility consisting of a metal tank made on the spot, a flocculation basin and a sedimentation basin.

Other field trials are planned in Malawi through April and, if the experiment lives up to expectations, the Leicester team will launch similar projects in other developing countries to try to alleviate water problems, now widespread in the Third World.

The World Health Organization (WHO) estimates that 1.2 billion people drink untreated water at considerable health risk. Eighty per cent live in small rural communities, where present-day treatment units require investments far beyond their means. Without gas cookers and with fuelwood in short supply, households cannot boil water to purify it. For young children, polluted water is the main cause of diarrhea and often fatal dehydration.

Corinne Bensimon